E-Mail

E-mail predates the internet, and was used by MIT as early as 1965 for stock exchange. Originally, email was transmitted directly from one user to another computer. This required both computers to be online at the same time. Today's email systems are based on a store-and-forward model. Email servers accept, forward, deliver and store messages. Users no longer need be online simultaneously and need only connect briefly, typically to an email server, for as long as it takes to send or receive messages.
An email message consists of two components, the message header, and the message body, which is the email's content. The message header contains control information, including, minimally, an originator's email address and one or more recipient addresses. Usually additional information is added, such as a subject header field.
The benefits are being instant, free and easy to store. However, both users need to have access to a computer and the account needs checking. Also spam (frequent advertising), phishing scans (con letters attempting to withdraw money or information) and viruses (attatched or hyperlinked files that can damage computers) are a problem. It is also impossible to e-mail a physical good, which has become the primary usage of traditional mail.
(SMTP) Simple Mail Transfer Protocol is the internet standard for email across internet protocol
POP (Post Office Protocol) is a system whereby emails are stored on third party servers and can be accessed by a user using an account from any computer, e.g) hotmail accounts.
Nowerdays smartphones and PCs can access e-mail from anywhere with connectivity allowing people to stay informed on the go.
However, I think the prominence of social networking sites are making e-mails considerably less popular as the more informal structure appeals to many and the greater layout prevents information overload and allows data to selectively be tracked down and organized. I do think e-mails will stay, but only for business and formalitys sake.